Joseph B, Lefebvre O, Méreau-Richard C, Danzé P M, Belin-Plancot M T, Formstecher P
INSERM U459 "Signaux, Récepteurs et Différenciation Cellulaire", Faculté de Médecine, Lille cedex, France.
Blood. 1998 Apr 1;91(7):2423-32.
In this study, we show that both all-trans-retinoic acid (atRA) and 9-cis-retinoic acid (9-cis-RA) are potent inducers of tissue transglutaminase (TGase II), an enzyme involved in apoptosis, at the level of both enzyme activity and mRNA in the human myeloma cell line RPMI 8226. RPMI 8226 cells were shown to express mRNAs for all the retinoid receptors subtypes, ie, RARalpha, RARbeta, RARgamma, RXRalpha, RXRbeta, and RXRgamma. To identify which of these receptors are involved in regulating TGase II expression, several receptor-selective synthetic retinoids were used. Neither CD367, a very potent retinoid that selectively binds and activates receptors of the RAR family, nor CD2425, an RXR-selective agonist, induced TGase II when used alone. However, combination of CD367 and CD2425 resulted in nearly full induction of the enzyme. Moreover, when used in combination with atRA, CD367 partially inhibited the atRA-dependent induction of TGase II, whereas CD2425 enhanced it. The effects of Am 580, CD417, and CD437, three synthetic retinoids selective for the RARs subtypes RARalpha, RARbeta, and RARgamma, respectively, were also investigated. None of these compounds was able to induce TGase II when used alone; however, the combination of each of them with CD2425 resulted in strong induction of the enzyme activity, reaching 30% to 50% of the values obtained in the presence of retinoic acid and suggesting functional redundancy between the RAR subtypes. Finally, treatment with atRA or the combination of CD367 and CD2425, but not with CD367 or CD2425 alone, was also shown to trigger apoptosis in RPMI 8226 cells, with prominent accumulation of TGase II immunoreactivity in apoptotic cells. Taken together these data suggest that the induction of TGase II expression and apoptosis in the RPMI 8226 myeloma cell line required ligand-dependent activation of both the RAR and RXR receptors.
在本研究中，我们发现全反式维甲酸（atRA）和9-顺式维甲酸（9-cis-RA）在人骨髓瘤细胞系RPMI 8226中，在酶活性和mRNA水平上都是组织转谷氨酰胺酶（TGase II）的有效诱导剂，该酶参与细胞凋亡。RPMI 8226细胞被证明表达所有类视黄醇受体亚型的mRNA，即RARα、RARβ、RARγ、RXRα、RXRβ和RXRγ。为了确定这些受体中哪些参与调节TGase II的表达，使用了几种受体选择性合成类视黄醇。单独使用时，CD367（一种非常有效的类视黄醇，可选择性结合并激活RAR家族的受体）和CD2425（一种RXR选择性激动剂）均未诱导TGase II。然而，CD367和CD2425联合使用可使该酶几乎完全被诱导。此外，当与atRA联合使用时，CD367部分抑制了atRA依赖性的TGase II诱导，而CD2425则增强了这种诱导。还研究了Am 580、CD417和CD437这三种分别对RAR亚型RARα、RARβ和RARγ具有选择性的合成类视黄醇的作用。单独使用这些化合物时均不能诱导TGase II；然而，它们中的每一种与CD2425联合使用均导致该酶活性的强烈诱导，达到在维甲酸存在下所获得值的30%至50%，这表明RAR亚型之间存在功能冗余。最后，单独使用atRA或CD367与CD2425联合使用，但不单独使用CD367或CD2425，也被证明可触发RPMI 8226细胞凋亡，凋亡细胞中TGase II免疫反应性显著积累。综上所述，这些数据表明，RPMI 8226骨髓瘤细胞系中TGase II表达的诱导和细胞凋亡需要RAR和RXR受体的配体依赖性激活。
